import { ALPHABET_BY_LETTER, LETTERS_UPPER } from '../../../core/data/alphabet';

/** 字母描红的布局模式（与产品文档四类练习一致） */
export type LetterTracingMode =
    /** 4 看图描红：教学区 + 6 行描红（前三行大写、后三行小写） */
    | 'picture-tracing'
    /** 1 大小写配对：左栏 A–M、右栏 N–Z，每行最多 4 组 Aa */
    | 'case-pairing'
    /** 2 分栏对照：半组字母，左栏大写、右栏小写，每行 4 个 */
    | 'column-compare'
    /** 3 字母总览：Uppercase / Lowercase 分区，每区 9+9+8 */
    | 'overview';

/** 字母大小写模式（部分模式不使用） */
export type LetterCaseMode = 'upper' | 'lower' | 'both';

/** A–M / N–Z 半表（分栏对照） */
export type AlphabetHalf = 'A-M' | 'N-Z';

/** 字母描红生成器的配置项 */
export interface LetterTracingGeneratorConfig {
    mode: LetterTracingMode;
    letterCase: LetterCaseMode;
    selectedLetter?: string;
    repetitions: number;
    fadePattern: 'gradient' | 'first-only';
    /** 分栏对照：练习 A–M 或 N–Z */
    alphabetHalf?: AlphabetHalf;
}

/** 单个描红格子的数据 */
export interface TracingCell {
    char: string;
    opacity: number;
    isGuide: boolean;
    /** 与 char 组成大小写一对（如 A + a），用于大小写配对格内展示 */
    pairChar?: string;
}

/** 一行描红数据，包含展示字符和若干格子 */
export interface TracingRow {
    displayChar: string;
    cells: TracingCell[];
}

/** 看图描红教学区 */
export interface TeachingBlock {
    upper: string;
    lower: string;
    word: string;
    sentence: string;
    emoji: string;
}

export type LetterTracingData =
    | {
          mode: 'picture-tracing';
          teaching: TeachingBlock;
          rows: TracingRow[];
      }
    | {
          mode: 'case-pairing';
          leftVisualRows: TracingRow[][];
          rightVisualRows: TracingRow[][];
      }
    | {
          mode: 'column-compare';
          leftRows: TracingRow[];
          rightRows: TracingRow[];
      }
    | {
          mode: 'overview';
          upperRows: string[][];
          lowerRows: string[][];
      };

/** 将用户输入的字母标准化为大写单字符，默认 'A' */
export function normalizeLetter(c: string): string {
    const u = c.trim().toUpperCase();
    return u.length ? u[0] : 'A';
}

function buildCells(
    char: string,
    count: number,
    fadePattern: 'gradient' | 'first-only',
    pairChar?: string,
): TracingCell[] {
    const n = Math.max(1, Math.min(12, count));
    const cells: TracingCell[] = [];
    for (let i = 0; i < n; i++) {
        let opacity: number;
        if (fadePattern === 'first-only') {
            opacity = i === 0 ? 1 : 0;
        } else if (n <= 1) {
            opacity = 1;
        } else {
            opacity = Math.max(0.12, 1 - i / (n - 1));
        }
        cells.push({
            char,
            opacity,
            isGuide: i === 0,
            ...(pairChar !== undefined ? { pairChar } : {}),
        });
    }
    return cells;
}

function rowForChar(
    ch: string,
    repetitions: number,
    fadePattern: 'gradient' | 'first-only',
    pairChar?: string,
): TracingRow {
    return {
        displayChar: ch,
        cells: buildCells(ch, repetitions, fadePattern, pairChar),
    };
}

/** 一行内多个字母，各自占一段描红格（用于分栏对照等） */
function rowForManyChars(
    chars: string[],
    repetitions: number,
    fadePattern: 'gradient' | 'first-only',
): TracingRow {
    const cells: TracingCell[] = [];
    for (const ch of chars) {
        cells.push(...buildCells(ch, repetitions, fadePattern));
    }
    return {
        displayChar: chars.join(''),
        cells,
    };
}

function chunk<T>(arr: T[], size: number): T[][] {
    const out: T[][] = [];
    for (let i = 0; i < arr.length; i += size) {
        out.push(arr.slice(i, i + size));
    }
    return out;
}

/** 总览区 26 字母拆成 9 + 9 + 8 三行 */
function overviewRowsFrom(letters: string[]): string[][] {
    return [letters.slice(0, 9), letters.slice(9, 18), letters.slice(18, 26)];
}

/**
 * 根据配置生成字母描红数据
 * - picture-tracing：教学区 + 6 行描红
 * - case-pairing：左 A–M / 右 N–Z，每行最多 4 组大小写配对
 * - column-compare：半表，左大写右小写，每行 4 个
 * - overview：Uppercase / Lowercase Letters，9+9+8
 */
export function generateLetterTracing(
    config: LetterTracingGeneratorConfig,
): LetterTracingData {
    const { mode, repetitions, fadePattern } = config;

    if (mode === 'picture-tracing') {
        const key = normalizeLetter(config.selectedLetter ?? 'A');
        const meta = ALPHABET_BY_LETTER[key] ?? ALPHABET_BY_LETTER.A;
        const upper = key;
        const lower = key.toLowerCase();
        const teaching: TeachingBlock = {
            upper,
            lower,
            word: meta.word,
            sentence: `${upper} is for ${meta.word}`,
            emoji: meta.emoji,
        };
        const rows: TracingRow[] = [
            rowForChar(upper, repetitions, fadePattern),
            rowForChar(upper, repetitions, fadePattern),
            rowForChar(upper, repetitions, fadePattern),
            rowForChar(lower, repetitions, fadePattern),
            rowForChar(lower, repetitions, fadePattern),
            rowForChar(lower, repetitions, fadePattern),
        ];
        return { mode: 'picture-tracing', teaching, rows };
    }

    if (mode === 'case-pairing') {
        const leftLetters = LETTERS_UPPER.slice(0, 13);
        const rightLetters = LETTERS_UPPER.slice(13);
        const pack = (letters: string[]) =>
            chunk(letters, 4).map((group) =>
                group.map((L) =>
                    rowForChar(
                        L,
                        repetitions,
                        fadePattern,
                        L.toLowerCase(),
                    ),
                ),
            );
        return {
            mode: 'case-pairing',
            leftVisualRows: pack(leftLetters),
            rightVisualRows: pack(rightLetters),
        };
    }

    if (mode === 'column-compare') {
        const half =
            config.alphabetHalf === 'N-Z'
                ? LETTERS_UPPER.slice(13)
                : LETTERS_UPPER.slice(0, 13);
        const rowsOf4 = chunk(half, 4);
        const leftRows = rowsOf4.map((g) =>
            rowForManyChars(g, repetitions, fadePattern),
        );
        const rightRows = rowsOf4.map((g) =>
            rowForManyChars(
                g.map((L) => L.toLowerCase()),
                repetitions,
                fadePattern,
            ),
        );
        return { mode: 'column-compare', leftRows, rightRows };
    }

    // overview
    return {
        mode: 'overview',
        upperRows: overviewRowsFrom([...LETTERS_UPPER]),
        lowerRows: overviewRowsFrom(
            LETTERS_UPPER.map((L) => L.toLowerCase()),
        ),
    };
}

/** 与 WorksheetDefinition.generatorConfig 合并后的运行时配置 */
export function mergeLetterTracingConfig(
    base: Partial<LetterTracingGeneratorConfig>,
    overrides: Partial<LetterTracingGeneratorConfig>,
): LetterTracingGeneratorConfig {
    return {
        mode: (overrides.mode ??
            base.mode ??
            'picture-tracing') as LetterTracingMode,
        letterCase: (overrides.letterCase ??
            base.letterCase ??
            'upper') as LetterCaseMode,
        selectedLetter: overrides.selectedLetter ?? base.selectedLetter,
        repetitions: Math.max(
            1,
            (overrides.repetitions ?? base.repetitions ?? 5) as number,
        ),
        fadePattern: (overrides.fadePattern ??
            base.fadePattern ??
            'gradient') as 'gradient' | 'first-only',
        alphabetHalf: (overrides.alphabetHalf ??
            base.alphabetHalf ??
            'A-M') as AlphabetHalf,
    };
}