photon-ui 0.4.5

//! ANSI escape sequence generation for RGB colors.
//!
//! Supports three rendering modes:
//! - **TrueColor** (24-bit RGB) — default, best quality
//! - **Color256** — xterm 256-color cube fallback
//! - **Basic16** — coarse 16-color fallback

use std::env;

use super::Color;

/// Terminal color support level.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
pub enum ColorMode {
    /// 24-bit RGB (`\x1b[38;2;R;G;Bm`).
    #[default]
    TrueColor,
    /// xterm 256-color palette (`\x1b[38;5;Nm`).
    Color256,
    /// ANSI 16-color (`\x1b[30m`–`\x1b[37m`, `\x1b[90m`–`\x1b[97m`).
    Basic16,
}

impl ColorMode {
    /// Detect the best available color mode from environment variables.
    ///
    /// Checks `PHOTON_COLOR_MODE` first, then `COLORTERM`, then `TERM`.
    pub fn detect() -> Self {
        if let Ok(mode) = env::var("PHOTON_COLOR_MODE") {
            match mode.as_str() {
                | "truecolor" | "24bit" | "rgb" => return ColorMode::TrueColor,
                | "256" | "256color" => return ColorMode::Color256,
                | "16" | "basic" => return ColorMode::Basic16,
                | _ => {},
            }
        }
        if let Ok(ct) = env::var("COLORTERM") &&
            (ct == "truecolor" || ct == "24bit")
        {
            return ColorMode::TrueColor;
        }
        if let Ok(term) = env::var("TERM") &&
            term.contains("256color")
        {
            return ColorMode::Color256;
        }
        ColorMode::TrueColor
    }
}

/// Generate a foreground ANSI escape sequence for the given color.
pub fn fg(color: Color, mode: ColorMode) -> String {
    match mode {
        | ColorMode::TrueColor => format!("\x1b[38;2;{};{};{}m", color.0, color.1, color.2),
        | ColorMode::Color256 => format!("\x1b[38;5;{}m", rgb_to_256(color)),
        | ColorMode::Basic16 => format!("\x1b[{}m", rgb_to_16_fg(color)),
    }
}

/// Generate a background ANSI escape sequence for the given color.
pub fn bg(color: Color, mode: ColorMode) -> String {
    match mode {
        | ColorMode::TrueColor => format!("\x1b[48;2;{};{};{}m", color.0, color.1, color.2),
        | ColorMode::Color256 => format!("\x1b[48;5;{}m", rgb_to_256(color)),
        | ColorMode::Basic16 => format!("\x1b[{}m", rgb_to_16_bg(color)),
    }
}

/// Reset all ANSI attributes.
pub const RESET: &str = "\x1b[0m";

// ── 256-color conversion ──────────────────────────────────────────

fn rgb_to_256(color: Color) -> u8 {
    let Color(r, g, b) = color;

    // Check if grayscale
    if r == g && g == b {
        if r < 8 {
            return 16;
        }
        if r > 248 {
            return 231;
        }
        return 232 + ((r - 8) / 10);
    }

    // 6x6x6 color cube
    let r = closest_cube_level(r);
    let g = closest_cube_level(g);
    let b = closest_cube_level(b);
    16 + 36 * r + 6 * g + b
}

fn closest_cube_level(v: u8) -> u8 {
    // Levels: 0, 95, 135, 175, 215, 255
    if v < 48 {
        0
    } else if v < 115 {
        1
    } else if v < 155 {
        2
    } else if v < 195 {
        3
    } else if v < 235 {
        4
    } else {
        5
    }
}

// ── 16-color conversion ───────────────────────────────────────────

fn rgb_to_16_fg(color: Color) -> u8 {
    30 + rgb_to_16_index(color)
}

fn rgb_to_16_bg(color: Color) -> u8 {
    40 + rgb_to_16_index(color)
}

fn rgb_to_16_index(color: Color) -> u8 {
    let Color(r, g, b) = color;
    let intensity = (r as u16 + g as u16 + b as u16) / 3;

    // Simple nearest-match to ANSI 8 colors + bright variants
    let is_bright = intensity > 128;
    let idx = if r > 128 && g < 128 && b < 128 {
        1 // red
    } else if r < 128 && g > 128 && b < 128 {
        2 // green
    } else if r > 128 && g > 128 && b < 128 {
        3 // yellow
    } else if r < 128 && g < 128 && b > 128 {
        4 // blue
    } else if r > 128 && g < 128 && b > 128 {
        5 // magenta
    } else if r < 128 && g > 128 && b > 128 {
        6 // cyan
    } else {
        0 // black/white
    };

    if is_bright && idx == 0 {
        7 // bright white
    } else if is_bright {
        idx + 60 // bright variant (90-97)
    } else {
        idx
    }
}

#[cfg(test)]
mod tests {
    use std::{
        env,
        sync::Mutex,
    };

    use super::*;

    // Environment variables are process-wide, so env-mutating tests must be
    // serialized even when cargo runs other tests in parallel.
    static ENV_LOCK: Mutex<()> = Mutex::new(());

    fn with_envs<F>(vars: &[(&str, Option<&str>)], f: F)
    where
        F: FnOnce(), {
        let _guard = ENV_LOCK.lock().unwrap();
        let originals: Vec<(String, Option<String>)> = vars
            .iter()
            .map(|(key, _)| ((*key).to_string(), env::var(key).ok()))
            .collect();
        for (key, value) in vars {
            match value {
                // SAFETY: tests that mutate env vars are serialized via ENV_LOCK.
                | Some(v) => unsafe { env::set_var(key, v) },
                // SAFETY: same as above — serialized env mutation.
                | None => unsafe { env::remove_var(key) },
            }
        }
        f();
        for (key, original) in originals {
            match original {
                // SAFETY: serialized env mutation.
                | Some(v) => unsafe { env::set_var(&key, v) },
                // SAFETY: serialized env mutation.
                | None => unsafe { env::remove_var(&key) },
            }
        }
    }

    #[test]
    fn truecolor_fg() {
        let s = fg(Color::SUNBEAM_ORANGE, ColorMode::TrueColor);
        assert_eq!(s, "\x1b[38;2;250;82;15m");
    }

    #[test]
    fn truecolor_bg() {
        let s = bg(Color::WARM_IVORY, ColorMode::TrueColor);
        assert_eq!(s, "\x1b[48;2;255;250;237m");
    }

    #[test]
    fn color256_produces_valid_codes() {
        let s = fg(Color::SUNBEAM_ORANGE, ColorMode::Color256);
        assert!(s.starts_with("\x1b[38;5;"));
        assert!(s.ends_with('m'));
    }

    #[test]
    fn color256_bg_produces_valid_codes() {
        let s = bg(Color::SUNBEAM_ORANGE, ColorMode::Color256);
        assert!(s.starts_with("\x1b[48;5;"));
        assert!(s.ends_with('m'));
    }

    #[test]
    fn basic16_produces_valid_codes() {
        let s = fg(Color::WHITE, ColorMode::Basic16);
        assert!(s.starts_with("\x1b["));
        assert!(s.ends_with('m'));
    }

    #[test]
    fn basic16_bg_produces_valid_codes() {
        let s = bg(Color::WHITE, ColorMode::Basic16);
        assert!(s.starts_with("\x1b["));
        assert!(s.ends_with('m'));
    }

    #[test]
    fn detect_respects_photon_color_mode() {
        with_envs(&[("PHOTON_COLOR_MODE", Some("256"))], || {
            assert_eq!(ColorMode::detect(), ColorMode::Color256);
        });
        with_envs(&[("PHOTON_COLOR_MODE", Some("basic"))], || {
            assert_eq!(ColorMode::detect(), ColorMode::Basic16);
        });
        with_envs(&[("PHOTON_COLOR_MODE", Some("truecolor"))], || {
            assert_eq!(ColorMode::detect(), ColorMode::TrueColor);
        });
        with_envs(
            &[
                ("PHOTON_COLOR_MODE", Some("unknown")),
                ("COLORTERM", None),
                ("TERM", None),
            ],
            || {
                assert_eq!(ColorMode::detect(), ColorMode::TrueColor);
            },
        );
    }

    #[test]
    fn detect_respects_colorterm() {
        with_envs(
            &[
                ("PHOTON_COLOR_MODE", None),
                ("COLORTERM", Some("truecolor")),
                ("TERM", None),
            ],
            || {
                assert_eq!(ColorMode::detect(), ColorMode::TrueColor);
            },
        );
        with_envs(
            &[
                ("PHOTON_COLOR_MODE", None),
                ("COLORTERM", Some("24bit")),
                ("TERM", None),
            ],
            || {
                assert_eq!(ColorMode::detect(), ColorMode::TrueColor);
            },
        );
    }

    #[test]
    fn detect_respects_term() {
        with_envs(
            &[
                ("PHOTON_COLOR_MODE", None),
                ("COLORTERM", None),
                ("TERM", Some("xterm-256color")),
            ],
            || {
                assert_eq!(ColorMode::detect(), ColorMode::Color256);
            },
        );
        with_envs(
            &[
                ("PHOTON_COLOR_MODE", None),
                ("COLORTERM", None),
                ("TERM", Some("xterm")),
            ],
            || {
                assert_eq!(ColorMode::detect(), ColorMode::TrueColor);
            },
        );
    }

    #[test]
    fn rgb_to_256_grayscale() {
        assert_eq!(rgb_to_256(Color(0, 0, 0)), 16);
        assert_eq!(rgb_to_256(Color(255, 255, 255)), 231);
        assert_eq!(rgb_to_256(Color(128, 128, 128)), 232 + ((128 - 8) / 10));
    }

    #[test]
    fn rgb_to_256_color_cube() {
        // SUNBEAM_ORANGE is not grayscale, so it should map into the 6x6x6 cube.
        let idx = rgb_to_256(Color::SUNBEAM_ORANGE);
        assert!((16..=231).contains(&idx));
    }

    #[test]
    fn closest_cube_level_branches() {
        assert_eq!(closest_cube_level(0), 0);
        assert_eq!(closest_cube_level(47), 0);
        assert_eq!(closest_cube_level(48), 1);
        assert_eq!(closest_cube_level(114), 1);
        assert_eq!(closest_cube_level(115), 2);
        assert_eq!(closest_cube_level(154), 2);
        assert_eq!(closest_cube_level(155), 3);
        assert_eq!(closest_cube_level(194), 3);
        assert_eq!(closest_cube_level(195), 4);
        assert_eq!(closest_cube_level(234), 4);
        assert_eq!(closest_cube_level(235), 5);
        assert_eq!(closest_cube_level(255), 5);
    }

    #[test]
    fn rgb_to_16_fg_and_bg() {
        // White maps to bright white (7) for fg, so 37; for bg, 47.
        assert_eq!(rgb_to_16_fg(Color::WHITE), 37);
        assert_eq!(rgb_to_16_bg(Color::WHITE), 47);
    }

    #[test]
    fn rgb_to_16_index_color_branches() {
        // Red (average intensity 85, not bright -> idx 1)
        assert_eq!(rgb_to_16_index(Color(255, 0, 0)), 1);
        // Green (average intensity 85, not bright -> idx 2)
        assert_eq!(rgb_to_16_index(Color(0, 255, 0)), 2);
        // Yellow (average intensity 170, bright -> idx 3 + 60 = 63)
        assert_eq!(rgb_to_16_index(Color(255, 255, 0)), 63);
        // Blue (average intensity 85, not bright -> idx 4)
        assert_eq!(rgb_to_16_index(Color(0, 0, 255)), 4);
        // Magenta (average intensity 170, bright -> idx 5 + 60 = 65)
        assert_eq!(rgb_to_16_index(Color(255, 0, 255)), 65);
        // Cyan (average intensity 170, bright -> idx 6 + 60 = 66)
        assert_eq!(rgb_to_16_index(Color(0, 255, 255)), 66);
        // Black (low intensity -> index 0)
        assert_eq!(rgb_to_16_index(Color(0, 0, 0)), 0);
        // White (high intensity, idx 0 -> bright white 7)
        assert_eq!(rgb_to_16_index(Color(255, 255, 255)), 7);
        // Dim red (r > 128 but average intensity <= 128 -> idx 1)
        assert_eq!(rgb_to_16_index(Color(192, 0, 0)), 1);
    }
}