use crate::memory::MemoryCreator;
use crate::trampoline::MemoryCreatorProxy;
use anyhow::{bail, Result};
use std::cmp;
use std::convert::TryFrom;
use std::fmt;
#[cfg(feature = "cache")]
use std::path::Path;
use std::sync::Arc;
use wasmparser::WasmFeatures;
#[cfg(feature = "cache")]
use wasmtime_cache::CacheConfig;
use wasmtime_environ::settings::{self, Configurable, SetError};
use wasmtime_environ::{isa, isa::TargetIsa, Tunables};
use wasmtime_jit::{native, CompilationStrategy, Compiler};
use wasmtime_profiling::{JitDumpAgent, NullProfilerAgent, ProfilingAgent, VTuneAgent};

/// Global configuration options used to create an [`Engine`](crate::Engine)
/// and customize its behavior.
///
/// This structure exposed a builder-like interface and is primarily consumed by
/// [`Engine::new()`](crate::Engine::new)
#[derive(Clone)]
pub struct Config {
    pub(crate) flags: settings::Builder,
    pub(crate) isa_flags: isa::Builder,
    pub(crate) tunables: Tunables,
    pub(crate) strategy: CompilationStrategy,
    #[cfg(feature = "cache")]
    pub(crate) cache_config: CacheConfig,
    pub(crate) profiler: Arc<dyn ProfilingAgent>,
    pub(crate) memory_creator: Option<MemoryCreatorProxy>,
    pub(crate) max_wasm_stack: usize,
    pub(crate) features: WasmFeatures,
    pub(crate) wasm_backtrace_details_env_used: bool,
    pub(crate) max_instances: usize,
    pub(crate) max_tables: usize,
    pub(crate) max_memories: usize,
}

impl Config {
    /// Creates a new configuration object with the default configuration
    /// specified.
    pub fn new() -> Config {
        let mut flags = settings::builder();

        // There are two possible traps for division, and this way
        // we get the proper one if code traps.
        flags
            .enable("avoid_div_traps")
            .expect("should be valid flag");

        // Invert cranelift's default-on verification to instead default off.
        flags
            .set("enable_verifier", "false")
            .expect("should be valid flag");

        // Turn on cranelift speed optimizations by default
        flags
            .set("opt_level", "speed")
            .expect("should be valid flag");

        // We don't use probestack as a stack limit mechanism
        flags
            .set("enable_probestack", "false")
            .expect("should be valid flag");

        let mut ret = Config {
            tunables: Tunables::default(),
            flags,
            isa_flags: native::builder(),
            strategy: CompilationStrategy::Auto,
            #[cfg(feature = "cache")]
            cache_config: CacheConfig::new_cache_disabled(),
            profiler: Arc::new(NullProfilerAgent),
            memory_creator: None,
            max_wasm_stack: 1 << 20,
            wasm_backtrace_details_env_used: false,
            features: WasmFeatures {
                reference_types: true,
                bulk_memory: true,
                multi_value: true,
                ..WasmFeatures::default()
            },
            max_instances: 10_000,
            max_tables: 10_000,
            max_memories: 10_000,
        };
        ret.wasm_backtrace_details(WasmBacktraceDetails::Environment);
        return ret;
    }

    /// Configures whether DWARF debug information will be emitted during
    /// compilation.
    ///
    /// By default this option is `false`.
    pub fn debug_info(&mut self, enable: bool) -> &mut Self {
        self.tunables.generate_native_debuginfo = enable;
        self
    }

    /// Configures backtraces in `Trap` will parse debuginfo in the wasm file to
    /// have filename/line number information.
    ///
    /// When enabled this will causes modules to retain debugging information
    /// found in wasm binaries. This debug information will be used when a trap
    /// happens to symbolicate each stack frame and attempt to print a
    /// filename/line number for each wasm frame in the stack trace.
    ///
    /// By default this option is `WasmBacktraceDetails::Environment`, meaning
    /// that wasm will read `WASMTIME_BACKTRACE_DETAILS` to indicate whether details
    /// should be parsed.
    pub fn wasm_backtrace_details(&mut self, enable: WasmBacktraceDetails) -> &mut Self {
        self.wasm_backtrace_details_env_used = false;
        self.tunables.parse_wasm_debuginfo = match enable {
            WasmBacktraceDetails::Enable => true,
            WasmBacktraceDetails::Disable => false,
            WasmBacktraceDetails::Environment => {
                self.wasm_backtrace_details_env_used = true;
                std::env::var("WASMTIME_BACKTRACE_DETAILS")
                    .map(|s| s == "1")
                    .unwrap_or(false)
            }
        };
        self
    }

    /// Configures whether functions and loops will be interruptable via the
    /// [`Store::interrupt_handle`](crate::Store::interrupt_handle) method.
    ///
    /// For more information see the documentation on
    /// [`Store::interrupt_handle`](crate::Store::interrupt_handle).
    ///
    /// By default this option is `false`.
    pub fn interruptable(&mut self, enable: bool) -> &mut Self {
        self.tunables.interruptable = enable;
        self
    }

    /// Configures whether execution of WebAssembly will "consume fuel" to
    /// either halt or yield execution as desired.
    ///
    /// This option is similar in purpose to [`Config::interruptable`] where
    /// you can prevent infinitely-executing WebAssembly code. The difference
    /// is that this option allows deterministic execution of WebAssembly code
    /// by instrumenting generated code consume fuel as it executes. When fuel
    /// runs out the behavior is defined by configuration within a [`Store`],
    /// and by default a trap is raised.
    ///
    /// Note that a [`Store`] starts with no fuel, so if you enable this option
    /// you'll have to be sure to pour some fuel into [`Store`] before
    /// executing some code.
    ///
    /// By default this option is `false`.
    ///
    /// [`Store`]: crate::Store
    pub fn consume_fuel(&mut self, enable: bool) -> &mut Self {
        self.tunables.consume_fuel = enable;
        self
    }

    /// Configures the maximum amount of native stack space available to
    /// executing WebAssembly code.
    ///
    /// WebAssembly code currently executes on the native call stack for its own
    /// call frames. WebAssembly, however, also has well-defined semantics on
    /// stack overflow. This is intended to be a knob which can help configure
    /// how much native stack space a wasm module is allowed to consume. Note
    /// that the number here is not super-precise, but rather wasm will take at
    /// most "pretty close to this much" stack space.
    ///
    /// If a wasm call (or series of nested wasm calls) take more stack space
    /// than the `size` specified then a stack overflow trap will be raised.
    ///
    /// By default this option is 1 MB.
    pub fn max_wasm_stack(&mut self, size: usize) -> &mut Self {
        self.max_wasm_stack = size;
        self
    }

    /// Configures whether the WebAssembly threads proposal will be enabled for
    /// compilation.
    ///
    /// The [WebAssembly threads proposal][threads] is not currently fully
    /// standardized and is undergoing development. Additionally the support in
    /// wasmtime itself is still being worked on. Support for this feature can
    /// be enabled through this method for appropriate wasm modules.
    ///
    /// This feature gates items such as shared memories and atomic
    /// instructions. Note that enabling the threads feature will
    /// also enable the bulk memory feature.
    ///
    /// This is `false` by default.
    ///
    /// > **Note**: Wasmtime does not implement everything for the wasm threads
    /// > spec at this time, so bugs, panics, and possibly segfaults should be
    /// > expected. This should not be enabled in a production setting right
    /// > now.
    ///
    /// [threads]: https://github.com/webassembly/threads
    pub fn wasm_threads(&mut self, enable: bool) -> &mut Self {
        self.features.threads = enable;
        // The threads proposal depends on the bulk memory proposal
        if enable {
            self.wasm_bulk_memory(true);
        }
        self
    }

    /// Configures whether the [WebAssembly reference types proposal][proposal]
    /// will be enabled for compilation.
    ///
    /// This feature gates items such as the `externref` and `funcref` types as
    /// well as allowing a module to define multiple tables.
    ///
    /// Note that enabling the reference types feature will also enable the bulk
    /// memory feature.
    ///
    /// This is `true` by default on x86-64, and `false` by default on other
    /// architectures.
    ///
    /// [proposal]: https://github.com/webassembly/reference-types
    pub fn wasm_reference_types(&mut self, enable: bool) -> &mut Self {
        self.features.reference_types = enable;

        self.flags
            .set("enable_safepoints", if enable { "true" } else { "false" })
            .unwrap();

        // The reference types proposal depends on the bulk memory proposal.
        if enable {
            self.wasm_bulk_memory(true);
        }

        self
    }

    /// Configures whether the WebAssembly SIMD proposal will be
    /// enabled for compilation.
    ///
    /// The [WebAssembly SIMD proposal][proposal] is not currently
    /// fully standardized and is undergoing development. Additionally the
    /// support in wasmtime itself is still being worked on. Support for this
    /// feature can be enabled through this method for appropriate wasm
    /// modules.
    ///
    /// This feature gates items such as the `v128` type and all of its
    /// operators being in a module.
    ///
    /// This is `false` by default.
    ///
    /// > **Note**: Wasmtime does not implement everything for the wasm simd
    /// > spec at this time, so bugs, panics, and possibly segfaults should be
    /// > expected. This should not be enabled in a production setting right
    /// > now.
    ///
    /// [proposal]: https://github.com/webassembly/simd
    pub fn wasm_simd(&mut self, enable: bool) -> &mut Self {
        self.features.simd = enable;
        let val = if enable { "true" } else { "false" };
        self.flags
            .set("enable_simd", val)
            .expect("should be valid flag");
        self
    }

    /// Configures whether the [WebAssembly bulk memory operations
    /// proposal][proposal] will be enabled for compilation.
    ///
    /// This feature gates items such as the `memory.copy` instruction, passive
    /// data/table segments, etc, being in a module.
    ///
    /// This is `true` by default.
    ///
    /// [proposal]: https://github.com/webassembly/bulk-memory-operations
    pub fn wasm_bulk_memory(&mut self, enable: bool) -> &mut Self {
        self.features.bulk_memory = enable;
        self
    }

    /// Configures whether the WebAssembly multi-value [proposal] will
    /// be enabled for compilation.
    ///
    /// This feature gates functions and blocks returning multiple values in a
    /// module, for example.
    ///
    /// This is `true` by default.
    ///
    /// [proposal]: https://github.com/webassembly/multi-value
    pub fn wasm_multi_value(&mut self, enable: bool) -> &mut Self {
        self.features.multi_value = enable;
        self
    }

    /// Configures whether the WebAssembly multi-memory [proposal] will
    /// be enabled for compilation.
    ///
    /// This feature gates modules having more than one linear memory
    /// declaration or import.
    ///
    /// This is `false` by default.
    ///
    /// [proposal]: https://github.com/webassembly/multi-memory
    pub fn wasm_multi_memory(&mut self, enable: bool) -> &mut Self {
        self.features.multi_memory = enable;
        self
    }

    /// Configures whether the WebAssembly module linking [proposal] will
    /// be enabled for compilation.
    ///
    /// Note that development of this feature is still underway, so enabling
    /// this is likely to be full of bugs.
    ///
    /// This is `false` by default.
    ///
    /// [proposal]: https://github.com/webassembly/module-linking
    pub fn wasm_module_linking(&mut self, enable: bool) -> &mut Self {
        self.features.module_linking = enable;
        self
    }

    /// Configures which compilation strategy will be used for wasm modules.
    ///
    /// This method can be used to configure which compiler is used for wasm
    /// modules, and for more documentation consult the [`Strategy`] enumeration
    /// and its documentation.
    ///
    /// The default value for this is `Strategy::Auto`.
    ///
    /// # Errors
    ///
    /// Some compilation strategies require compile-time options of `wasmtime`
    /// itself to be set, but if they're not set and the strategy is specified
    /// here then an error will be returned.
    pub fn strategy(&mut self, strategy: Strategy) -> Result<&mut Self> {
        self.strategy = match strategy {
            Strategy::Auto => CompilationStrategy::Auto,
            Strategy::Cranelift => CompilationStrategy::Cranelift,
            #[cfg(feature = "lightbeam")]
            Strategy::Lightbeam => CompilationStrategy::Lightbeam,
            #[cfg(not(feature = "lightbeam"))]
            Strategy::Lightbeam => {
                anyhow::bail!("lightbeam compilation strategy wasn't enabled at compile time");
            }
        };
        Ok(self)
    }

    /// Creates a default profiler based on the profiling strategy choosen
    ///
    /// Profiler creation calls the type's default initializer where the purpose is
    /// really just to put in place the type used for profiling.
    pub fn profiler(&mut self, profile: ProfilingStrategy) -> Result<&mut Self> {
        self.profiler = match profile {
            ProfilingStrategy::JitDump => Arc::new(JitDumpAgent::new()?) as Arc<dyn ProfilingAgent>,
            ProfilingStrategy::VTune => Arc::new(VTuneAgent::new()?) as Arc<dyn ProfilingAgent>,
            ProfilingStrategy::None => Arc::new(NullProfilerAgent),
        };
        Ok(self)
    }

    /// Configures whether the debug verifier of Cranelift is enabled or not.
    ///
    /// When Cranelift is used as a code generation backend this will configure
    /// it to have the `enable_verifier` flag which will enable a number of debug
    /// checks inside of Cranelift. This is largely only useful for the
    /// developers of wasmtime itself.
    ///
    /// The default value for this is `false`
    pub fn cranelift_debug_verifier(&mut self, enable: bool) -> &mut Self {
        let val = if enable { "true" } else { "false" };
        self.flags
            .set("enable_verifier", val)
            .expect("should be valid flag");
        self
    }

    /// Configures the Cranelift code generator optimization level.
    ///
    /// When the Cranelift code generator is used you can configure the
    /// optimization level used for generated code in a few various ways. For
    /// more information see the documentation of [`OptLevel`].
    ///
    /// The default value for this is `OptLevel::None`.
    pub fn cranelift_opt_level(&mut self, level: OptLevel) -> &mut Self {
        let val = match level {
            OptLevel::None => "none",
            OptLevel::Speed => "speed",
            OptLevel::SpeedAndSize => "speed_and_size",
        };
        self.flags
            .set("opt_level", val)
            .expect("should be valid flag");
        self
    }

    /// Configures whether Cranelift should perform a NaN-canonicalization pass.
    ///
    /// When Cranelift is used as a code generation backend this will configure
    /// it to replace NaNs with a single canonical value. This is useful for users
    /// requiring entirely deterministic WebAssembly computation.
    /// This is not required by the WebAssembly spec, so it is not enabled by default.
    ///
    /// The default value for this is `false`
    pub fn cranelift_nan_canonicalization(&mut self, enable: bool) -> &mut Self {
        let val = if enable { "true" } else { "false" };
        self.flags
            .set("enable_nan_canonicalization", val)
            .expect("should be valid flag");
        self
    }

    /// Clears native CPU flags inferred from the host.
    ///
    /// By default Wasmtime will tune generated code for the host that Wasmtime
    /// itself is running on. If you're compiling on one host, however, and
    /// shipping artifacts to another host then this behavior may not be
    /// desired. This function will clear all inferred native CPU features.
    ///
    /// To enable CPU features afterwards it's recommended to use the
    /// [`Config::cranelift_other_flag`] method.
    pub fn cranelift_clear_cpu_flags(&mut self) -> &mut Self {
        self.isa_flags = native::builder_without_flags();
        self
    }

    /// Allows settings another Cranelift flag defined by a flag name and value. This allows
    /// fine-tuning of Cranelift settings.
    ///
    /// Since Cranelift flags may be unstable, this method should not be considered to be stable
    /// either; other `Config` functions should be preferred for stability.
    ///
    /// Note that this is marked as unsafe, because setting the wrong flag might break invariants,
    /// resulting in execution hazards.
    ///
    /// # Errors
    ///
    /// This method can fail if the flag's name does not exist, or the value is not appropriate for
    /// the flag type.
    pub unsafe fn cranelift_other_flag(&mut self, name: &str, value: &str) -> Result<&mut Self> {
        if let Err(err) = self.flags.set(name, value) {
            match err {
                SetError::BadName(_) => {
                    // Try the target-specific flags.
                    self.isa_flags.set(name, value)?;
                }
                _ => bail!(err),
            }
        }
        Ok(self)
    }

    /// Loads cache configuration specified at `path`.
    ///
    /// This method will read the file specified by `path` on the filesystem and
    /// attempt to load cache configuration from it. This method can also fail
    /// due to I/O errors, misconfiguration, syntax errors, etc. For expected
    /// syntax in the configuration file see the [documentation online][docs].
    ///
    /// By default cache configuration is not enabled or loaded.
    ///
    /// This method is only available when the `cache` feature of this crate is
    /// enabled.
    ///
    /// # Errors
    ///
    /// This method can fail due to any error that happens when loading the file
    /// pointed to by `path` and attempting to load the cache configuration.
    ///
    /// [docs]: https://bytecodealliance.github.io/wasmtime/cli-cache.html
    #[cfg(feature = "cache")]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "cache")))]
    pub fn cache_config_load(&mut self, path: impl AsRef<Path>) -> Result<&mut Self> {
        self.cache_config = CacheConfig::from_file(Some(path.as_ref()))?;
        Ok(self)
    }

    /// Loads cache configuration from the system default path.
    ///
    /// This commit is the same as [`Config::cache_config_load`] except that it
    /// does not take a path argument and instead loads the default
    /// configuration present on the system. This is located, for example, on
    /// Unix at `$HOME/.config/wasmtime/config.toml` and is typically created
    /// with the `wasmtime config new` command.
    ///
    /// By default cache configuration is not enabled or loaded.
    ///
    /// This method is only available when the `cache` feature of this crate is
    /// enabled.
    ///
    /// # Errors
    ///
    /// This method can fail due to any error that happens when loading the
    /// default system configuration. Note that it is not an error if the
    /// default config file does not exist, in which case the default settings
    /// for an enabled cache are applied.
    ///
    /// [docs]: https://bytecodealliance.github.io/wasmtime/cli-cache.html
    #[cfg(feature = "cache")]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "cache")))]
    pub fn cache_config_load_default(&mut self) -> Result<&mut Self> {
        self.cache_config = CacheConfig::from_file(None)?;
        Ok(self)
    }

    /// Sets a custom memory creator
    pub fn with_host_memory(&mut self, mem_creator: Arc<dyn MemoryCreator>) -> &mut Self {
        self.memory_creator = Some(MemoryCreatorProxy { mem_creator });
        self
    }

    /// Configures the maximum size, in bytes, where a linear memory is
    /// considered static, above which it'll be considered dynamic.
    ///
    /// This function configures the threshold for wasm memories whether they're
    /// implemented as a dynamically relocatable chunk of memory or a statically
    /// located chunk of memory. The `max_size` parameter here is the size, in
    /// bytes, where if the maximum size of a linear memory is below `max_size`
    /// then it will be statically allocated with enough space to never have to
    /// move. If the maximum size of a linear memory is larger than `max_size`
    /// then wasm memory will be dynamically located and may move in memory
    /// through growth operations.
    ///
    /// Specifying a `max_size` of 0 means that all memories will be dynamic and
    /// may be relocated through `memory.grow`. Also note that if any wasm
    /// memory's maximum size is below `max_size` then it will still reserve
    /// `max_size` bytes in the virtual memory space.
    ///
    /// ## Static vs Dynamic Memory
    ///
    /// Linear memories represent contiguous arrays of bytes, but they can also
    /// be grown through the API and wasm instructions. When memory is grown if
    /// space hasn't been preallocated then growth may involve relocating the
    /// base pointer in memory. Memories in Wasmtime are classified in two
    /// different ways:
    ///
    /// * **static** - these memories preallocate all space necessary they'll
    ///   ever need, meaning that the base pointer of these memories is never
    ///   moved. Static memories may take more virtual memory space because of
    ///   pre-reserving space for memories.
    ///
    /// * **dynamic** - these memories are not preallocated and may move during
    ///   growth operations. Dynamic memories consume less virtual memory space
    ///   because they don't need to preallocate space for future growth.
    ///
    /// Static memories can be optimized better in JIT code because once the
    /// base address is loaded in a function it's known that we never need to
    /// reload it because it never changes, `memory.grow` is generally a pretty
    /// fast operation because the wasm memory is never relocated, and under
    /// some conditions bounds checks can be elided on memory accesses.
    ///
    /// Dynamic memories can't be quite as heavily optimized because the base
    /// address may need to be reloaded more often, they may require relocating
    /// lots of data on `memory.grow`, and dynamic memories require
    /// unconditional bounds checks on all memory accesses.
    ///
    /// ## Should you use static or dynamic memory?
    ///
    /// In general you probably don't need to change the value of this property.
    /// The defaults here are optimized for each target platform to consume a
    /// reasonable amount of physical memory while also generating speedy
    /// machine code.
    ///
    /// One of the main reasons you may want to configure this today is if your
    /// environment can't reserve virtual memory space for each wasm linear
    /// memory. On 64-bit platforms wasm memories require a 6GB reservation by
    /// default, and system limits may prevent this in some scenarios. In this
    /// case you may wish to force memories to be allocated dynamically meaning
    /// that the virtual memory footprint of creating a wasm memory should be
    /// exactly what's used by the wasm itself.
    ///
    /// For 32-bit memories a static memory must contain at least 4GB of
    /// reserved address space plus a guard page to elide any bounds checks at
    /// all. Smaller static memories will use similar bounds checks as dynamic
    /// memories.
    ///
    /// ## Default
    ///
    /// The default value for this property depends on the host platform. For
    /// 64-bit platforms there's lots of address space available, so the default
    /// configured here is 4GB. WebAssembly linear memories currently max out at
    /// 4GB which means that on 64-bit platforms Wasmtime by default always uses
    /// a static memory. This, coupled with a sufficiently sized guard region,
    /// should produce the fastest JIT code on 64-bit platforms, but does
    /// require a large address space reservation for each wasm memory.
    ///
    /// For 32-bit platforms this value defaults to 1GB. This means that wasm
    /// memories whose maximum size is less than 1GB will be allocated
    /// statically, otherwise they'll be considered dynamic.
    pub fn static_memory_maximum_size(&mut self, max_size: u64) -> &mut Self {
        let max_pages = max_size / u64::from(wasmtime_environ::WASM_PAGE_SIZE);
        self.tunables.static_memory_bound = u32::try_from(max_pages).unwrap_or(u32::max_value());
        self
    }

    /// Configures the size, in bytes, of the guard region used at the end of a
    /// static memory's address space reservation.
    ///
    /// All WebAssembly loads/stores are bounds-checked and generate a trap if
    /// they're out-of-bounds. Loads and stores are often very performance
    /// critical, so we want the bounds check to be as fast as possible!
    /// Accelerating these memory accesses is the motivation for a guard after a
    /// memory allocation.
    ///
    /// Memories (both static and dynamic) can be configured with a guard at the
    /// end of them which consists of unmapped virtual memory. This unmapped
    /// memory will trigger a memory access violation (e.g. segfault) if
    /// accessed. This allows JIT code to elide bounds checks if it can prove
    /// that an access, if out of bounds, would hit the guard region. This means
    /// that having such a guard of unmapped memory can remove the need for
    /// bounds checks in JIT code.
    ///
    /// For the difference between static and dynamic memories, see the
    /// [`Config::static_memory_maximum_size`].
    ///
    /// ## How big should the guard be?
    ///
    /// In general, like with configuring `static_memory_maximum_size`, you
    /// probably don't want to change this value from the defaults. Otherwise,
    /// though, the size of the guard region affects the number of bounds checks
    /// needed for generated wasm code. More specifically, loads/stores with
    /// immediate offsets will generate bounds checks based on how big the guard
    /// page is.
    ///
    /// For 32-bit memories a 4GB static memory is required to even start
    /// removing bounds checks. A 4GB guard size will guarantee that the module
    /// has zero bounds checks for memory accesses. A 2GB guard size will
    /// eliminate all bounds checks with an immediate offset less than 2GB. A
    /// guard size of zero means that all memory accesses will still have bounds
    /// checks.
    ///
    /// ## Default
    ///
    /// The default value for this property is 2GB on 64-bit platforms. This
    /// allows eliminating almost all bounds checks on loads/stores with an
    /// immediate offset of less than 2GB. On 32-bit platforms this defaults to
    /// 64KB.
    ///
    /// ## Static vs Dynamic Guard Size
    ///
    /// Note that for now the static memory guard size must be at least as large
    /// as the dynamic memory guard size, so configuring this property to be
    /// smaller than the dynamic memory guard size will have no effect.
    pub fn static_memory_guard_size(&mut self, guard_size: u64) -> &mut Self {
        let guard_size = round_up_to_pages(guard_size);
        let guard_size = cmp::max(guard_size, self.tunables.dynamic_memory_offset_guard_size);
        self.tunables.static_memory_offset_guard_size = guard_size;
        self
    }

    /// Configures the size, in bytes, of the guard region used at the end of a
    /// dynamic memory's address space reservation.
    ///
    /// For the difference between static and dynamic memories, see the
    /// [`Config::static_memory_maximum_size`]
    ///
    /// For more information about what a guard is, see the documentation on
    /// [`Config::static_memory_guard_size`].
    ///
    /// Note that the size of the guard region for dynamic memories is not super
    /// critical for performance. Making it reasonably-sized can improve
    /// generated code slightly, but for maximum performance you'll want to lean
    /// towards static memories rather than dynamic anyway.
    ///
    /// Also note that the dynamic memory guard size must be smaller than the
    /// static memory guard size, so if a large dynamic memory guard is
    /// specified then the static memory guard size will also be automatically
    /// increased.
    ///
    /// ## Default
    ///
    /// This value defaults to 64KB.
    pub fn dynamic_memory_guard_size(&mut self, guard_size: u64) -> &mut Self {
        let guard_size = round_up_to_pages(guard_size);
        self.tunables.dynamic_memory_offset_guard_size = guard_size;
        self.tunables.static_memory_offset_guard_size =
            cmp::max(guard_size, self.tunables.static_memory_offset_guard_size);
        self
    }

    /// Configures the maximum number of instances which can be created within
    /// this `Store`.
    ///
    /// Instantiation will fail with an error if this limit is exceeded.
    ///
    /// This value defaults to 10,000.
    pub fn max_instances(&mut self, instances: usize) -> &mut Self {
        self.max_instances = instances;
        self
    }

    /// Configures the maximum number of tables which can be created within
    /// this `Store`.
    ///
    /// Instantiation will fail with an error if this limit is exceeded.
    ///
    /// This value defaults to 10,000.
    pub fn max_tables(&mut self, tables: usize) -> &mut Self {
        self.max_tables = tables;
        self
    }

    /// Configures the maximum number of memories which can be created within
    /// this `Store`.
    ///
    /// Instantiation will fail with an error if this limit is exceeded.
    ///
    /// This value defaults to 10,000.
    pub fn max_memories(&mut self, memories: usize) -> &mut Self {
        self.max_memories = memories;
        self
    }

    pub(crate) fn target_isa(&self) -> Box<dyn TargetIsa> {
        self.isa_flags
            .clone()
            .finish(settings::Flags::new(self.flags.clone()))
    }

    pub(crate) fn target_isa_with_reference_types(&self) -> Box<dyn TargetIsa> {
        let mut flags = self.flags.clone();
        flags.set("enable_safepoints", "true").unwrap();
        self.isa_flags.clone().finish(settings::Flags::new(flags))
    }

    pub(crate) fn build_compiler(&self) -> Compiler {
        let isa = self.target_isa();
        Compiler::new(isa, self.strategy, self.tunables.clone(), self.features)
    }
}

fn round_up_to_pages(val: u64) -> u64 {
    let page_size = region::page::size() as u64;
    debug_assert!(page_size.is_power_of_two());
    val.checked_add(page_size - 1)
        .map(|val| val & !(page_size - 1))
        .unwrap_or(u64::max_value() / page_size + 1)
}

impl Default for Config {
    fn default() -> Config {
        Config::new()
    }
}

impl fmt::Debug for Config {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Config")
            .field("debug_info", &self.tunables.generate_native_debuginfo)
            .field("parse_wasm_debuginfo", &self.tunables.parse_wasm_debuginfo)
            .field("strategy", &self.strategy)
            .field("wasm_threads", &self.features.threads)
            .field("wasm_reference_types", &self.features.reference_types)
            .field("wasm_bulk_memory", &self.features.bulk_memory)
            .field("wasm_simd", &self.features.simd)
            .field("wasm_multi_value", &self.features.multi_value)
            .field("wasm_module_linking", &self.features.module_linking)
            .field(
                "flags",
                &settings::Flags::new(self.flags.clone()).to_string(),
            )
            .finish()
    }
}

/// Possible Compilation strategies for a wasm module.
///
/// This is used as an argument to the [`Config::strategy`] method.
#[non_exhaustive]
#[derive(Clone, Debug)]
pub enum Strategy {
    /// An indicator that the compilation strategy should be automatically
    /// selected.
    ///
    /// This is generally what you want for most projects and indicates that the
    /// `wasmtime` crate itself should make the decision about what the best
    /// code generator for a wasm module is.
    ///
    /// Currently this always defaults to Cranelift, but the default value will
    /// change over time.
    Auto,

    /// Currently the default backend, Cranelift aims to be a reasonably fast
    /// code generator which generates high quality machine code.
    Cranelift,

    /// A single-pass code generator that is faster than Cranelift but doesn't
    /// produce as high-quality code.
    ///
    /// To successfully pass this argument to [`Config::strategy`] the
    /// `lightbeam` feature of this crate must be enabled.
    Lightbeam,
}

/// Possible optimization levels for the Cranelift codegen backend.
#[non_exhaustive]
#[derive(Clone, Debug)]
pub enum OptLevel {
    /// No optimizations performed, minimizes compilation time by disabling most
    /// optimizations.
    None,
    /// Generates the fastest possible code, but may take longer.
    Speed,
    /// Similar to `speed`, but also performs transformations aimed at reducing
    /// code size.
    SpeedAndSize,
}

/// Select which profiling technique to support.
#[derive(Debug, Clone, Copy)]
pub enum ProfilingStrategy {
    /// No profiler support.
    None,

    /// Collect profiling info for "jitdump" file format, used with `perf` on
    /// Linux.
    JitDump,

    /// Collect profiling info using the "ittapi", used with `VTune` on Linux.
    VTune,
}

/// Select how wasm backtrace detailed information is handled.
#[derive(Debug, Clone, Copy)]
pub enum WasmBacktraceDetails {
    /// Support is unconditionally enabled and wasmtime will parse and read
    /// debug information.
    Enable,

    /// Support is disabled, and wasmtime will not parse debug information for
    /// backtrace details.
    Disable,

    /// Support for backtrace details is conditional on the
    /// `WASMTIME_BACKTRACE_DETAILS` environment variable.
    Environment,
}