truecalc-workbook 0.8.0

use std::hash::{Hash, Hasher};

use serde::de::Error as _;
use serde::ser::{Error as _, SerializeMap};
use serde::{Deserialize, Deserializer, Serialize, Serializer};

/// An evaluated cell value — one of the seven types of schema spec §6.
///
/// Wire encodings extend the published `@truecalc/core` npm shapes:
/// `{ "type": "number", "value": 1.5 }`, with `error` using an `error` key
/// (`{ "error": "#REF!", "type": "error" }`).
///
/// Invariants (schema spec §6 and §8):
/// - `Number` and `Date` are always finite — NaN and infinity are
///   unrepresentable; the serializer rejects them and the deserializer
///   refuses them. `-0.0` is normalized to `0.0` on deserialization, and
///   equality/hashing treat them as the same value.
/// - `Array` is row-major, rectangular, non-empty, larger than 1×1 (a 1×1
///   array is collapsed to its scalar element before storage, schema spec
///   §6), and holds only scalar values (never a nested `Array`). It appears
///   only as a spill anchor's value (schema spec §5).
#[derive(Debug, Clone, PartialEq)]
pub enum Value {
    /// Finite IEEE-754 f64.
    Number(f64),
    /// Any Unicode string.
    Text(String),
    /// A boolean.
    Boolean(bool),
    /// A spreadsheet error code, e.g. `#REF!`. Allowed codes are the
    /// engine's error set for the workbook's flavor (registry-driven).
    Error(String),
    /// An evaluated-empty result (a formula cell before first recalc, or a
    /// formula referencing an unauthored cell). Never used to pad the
    /// sparse grid.
    Empty,
    /// Row-major 2-D array of scalar values; a spill anchor's full
    /// evaluated array.
    Array(Vec<Vec<Value>>),
    /// A date as a serial number (fractional part = time of day). The epoch
    /// is implied by the workbook's engine flavor, never stored per-value.
    Date(f64),
}

/// Bit pattern of a finite f64 with `-0.0` normalized to `0.0`, so that
/// hashing agrees with `==` (schema spec §8: hash and float equality operate
/// on post-normalization bit patterns; sound because the serializer rejects NaN).
fn normalized_bits(x: f64) -> u64 {
    if x == 0.0 {
        0.0_f64.to_bits()
    } else {
        x.to_bits()
    }
}

impl Hash for Value {
    fn hash<H: Hasher>(&self, state: &mut H) {
        std::mem::discriminant(self).hash(state);
        match self {
            Value::Number(n) | Value::Date(n) => normalized_bits(*n).hash(state),
            Value::Text(s) => s.hash(state),
            Value::Boolean(b) => b.hash(state),
            Value::Error(code) => code.hash(state),
            Value::Empty => {}
            Value::Array(rows) => {
                rows.len().hash(state);
                for row in rows {
                    row.len().hash(state);
                    for v in row {
                        v.hash(state);
                    }
                }
            }
        }
    }
}

fn serialize_tagged_number<S: Serializer>(
    kind: &'static str,
    n: f64,
    serializer: S,
) -> Result<S::Ok, S::Error> {
    if !n.is_finite() {
        return Err(S::Error::custom(format!(
            "non-finite {kind} value cannot be serialized (schema spec §8)"
        )));
    }
    let n = if n == 0.0 { 0.0 } else { n };
    let mut map = serializer.serialize_map(Some(2))?;
    map.serialize_entry("type", kind)?;
    map.serialize_entry("value", &n)?;
    map.end()
}

impl Serialize for Value {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        match self {
            Value::Number(n) => serialize_tagged_number("number", *n, serializer),
            Value::Date(n) => serialize_tagged_number("date", *n, serializer),
            Value::Text(s) => {
                let mut map = serializer.serialize_map(Some(2))?;
                map.serialize_entry("type", "text")?;
                map.serialize_entry("value", s)?;
                map.end()
            }
            Value::Boolean(b) => {
                let mut map = serializer.serialize_map(Some(2))?;
                map.serialize_entry("type", "boolean")?;
                map.serialize_entry("value", b)?;
                map.end()
            }
            Value::Error(code) => {
                // Key is `error`, not `value`; emitted before `type` to match
                // canonical (JCS) key order.
                let mut map = serializer.serialize_map(Some(2))?;
                map.serialize_entry("error", code)?;
                map.serialize_entry("type", "error")?;
                map.end()
            }
            Value::Empty => {
                let mut map = serializer.serialize_map(Some(2))?;
                map.serialize_entry("type", "empty")?;
                map.serialize_entry("value", &())?;
                map.end()
            }
            Value::Array(rows) => {
                if rows.is_empty() || rows[0].is_empty() {
                    return Err(S::Error::custom("array value must be non-empty"));
                }
                if rows.len() == 1 && rows[0].len() == 1 {
                    return Err(S::Error::custom(
                        "a 1x1 array does not exist in serialized form; collapse it \
                         to its scalar element (schema spec §6)",
                    ));
                }
                let width = rows[0].len();
                for row in rows {
                    if row.len() != width {
                        return Err(S::Error::custom("array value must be rectangular"));
                    }
                    for v in row {
                        if matches!(v, Value::Array(_)) {
                            return Err(S::Error::custom(
                                "array elements must be scalar values (no nested arrays)",
                            ));
                        }
                    }
                }
                let mut map = serializer.serialize_map(Some(2))?;
                map.serialize_entry("type", "array")?;
                map.serialize_entry("value", rows)?;
                map.end()
            }
        }
    }
}

impl<'de> Deserialize<'de> for Value {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        // Buffer into a JSON tree first: the payload's parse depends on the
        // `type` tag, and non-canonical input may order keys arbitrarily.
        let raw = serde_json::Value::deserialize(deserializer)?;
        parse_value(&raw).map_err(D::Error::custom)
    }
}

fn parse_value(raw: &serde_json::Value) -> Result<Value, String> {
    let obj = match raw.as_object() {
        Some(obj) => obj,
        None => return Err("a cell value must be a JSON object".to_string()),
    };
    let kind = match obj.get("type").and_then(serde_json::Value::as_str) {
        Some(kind) => kind,
        None => return Err("a cell value requires a string \"type\" field".to_string()),
    };
    let payload_key = if kind == "error" { "error" } else { "value" };
    let payload = match obj.get(payload_key) {
        Some(payload) if obj.len() == 2 => payload,
        _ => {
            return Err(format!(
                "a {kind} value must have exactly the fields \"type\" and \"{payload_key}\""
            ));
        }
    };
    match kind {
        "number" => Ok(Value::Number(parse_finite_f64(payload, kind)?)),
        "date" => Ok(Value::Date(parse_finite_f64(payload, kind)?)),
        "text" => match payload.as_str() {
            Some(s) => Ok(Value::Text(s.to_owned())),
            None => Err("a text value must be a JSON string".to_string()),
        },
        "boolean" => match payload.as_bool() {
            Some(b) => Ok(Value::Boolean(b)),
            None => Err("a boolean value must be a JSON boolean".to_string()),
        },
        "error" => match payload.as_str() {
            Some(code) => Ok(Value::Error(code.to_owned())),
            None => Err("an error value must carry a string error code".to_string()),
        },
        "empty" => {
            if payload.is_null() {
                Ok(Value::Empty)
            } else {
                Err("an empty value must be JSON null".to_string())
            }
        }
        "array" => parse_array(payload),
        other => Err(format!("unknown value type {other:?}")),
    }
}

fn parse_finite_f64(payload: &serde_json::Value, kind: &str) -> Result<f64, String> {
    // `as_f64` is correctly rounded only because the crate enables serde_json's
    // `float_roundtrip` feature; without it, serde_json's default parser is off
    // by up to one ULP for some extreme exponents, which would break the
    // `to_json ∘ from_json = id` byte guarantee (the canonical bytes of the
    // reparsed value would differ in the last shortest-round-trip digit).
    let n = match payload.as_f64() {
        Some(n) => n,
        None => return Err(format!("a {kind} value must be a JSON number")),
    };
    if !n.is_finite() {
        return Err(format!(
            "non-finite {kind} value is forbidden (schema spec §8)"
        ));
    }
    // Normalize -0.0 to 0.0 at the value level (schema spec §8).
    Ok(if n == 0.0 { 0.0 } else { n })
}

fn parse_array(payload: &serde_json::Value) -> Result<Value, String> {
    let raw_rows = match payload.as_array() {
        Some(rows) => rows,
        None => return Err("an array value must be a 2-D JSON array".to_string()),
    };
    if raw_rows.is_empty() {
        return Err("array value must be non-empty".to_string());
    }
    let mut rows = Vec::with_capacity(raw_rows.len());
    let mut width = None;
    for raw_row in raw_rows {
        let raw_row = match raw_row.as_array() {
            Some(row) => row,
            None => return Err("array rows must be JSON arrays".to_string()),
        };
        if raw_row.is_empty() {
            return Err("array value must be non-empty".to_string());
        }
        match width {
            None => width = Some(raw_row.len()),
            Some(w) if w != raw_row.len() => {
                return Err("array value must be rectangular".to_string());
            }
            Some(_) => {}
        }
        let mut row = Vec::with_capacity(raw_row.len());
        for raw_elem in raw_row {
            let elem = parse_value(raw_elem)?;
            if matches!(elem, Value::Array(_)) {
                return Err("array elements must be scalar values (no nested arrays)".to_string());
            }
            row.push(elem);
        }
        rows.push(row);
    }
    if rows.len() == 1 && rows[0].len() == 1 {
        return Err(
            "a 1x1 array does not exist in serialized form; it must be collapsed \
             to its scalar element (schema spec §6)"
                .to_string(),
        );
    }
    Ok(Value::Array(rows))
}