import type {
    BitPackerSchema,
    PackingContext,
    PackingStrategy,
} from "@suaveplan/bitpacker";

type ConditionalOp = "==" | "!=" | "<" | "<=" | ">" | ">=" | "in" | "has";

interface IfShape {
    field: string;
    op: ConditionalOp;
    value: unknown;
}

interface ConditionalSchemaShape {
    _if?: IfShape;
    _when?: IfShape;
    _then: BitPackerSchema;
    _else?: BitPackerSchema;
}

const NO_BRANCH = Symbol("NO_BRANCH");

const VALID_OPS: readonly ConditionalOp[] = [
    "==",
    "!=",
    "<",
    "<=",
    ">",
    ">=",
    "in",
    "has",
];

function getPredicate(obj: {
    _if?: unknown;
    _when?: unknown;
}): IfShape | undefined {
    const raw = obj._if ?? obj._when;
    if (!raw || typeof raw !== "object") return undefined;
    const predicate = raw as {
        field?: unknown;
        op?: unknown;
        value?: unknown;
    };
    if (typeof predicate.field !== "string" || predicate.field.length === 0) {
        return undefined;
    }
    if (
        typeof predicate.op !== "string" ||
        !(VALID_OPS as readonly string[]).includes(predicate.op)
    ) {
        return undefined;
    }
    if (!("value" in predicate)) return undefined;
    return predicate as IfShape;
}

export function isConditionalSchema(
    schema: unknown
): schema is ConditionalSchemaShape {
    if (
        typeof schema !== "object" ||
        schema === null ||
        Array.isArray(schema)
    ) {
        return false;
    }
    const obj = schema as {
        _if?: unknown;
        _when?: unknown;
        _then?: unknown;
    };
    const predicate = getPredicate(obj);
    if (predicate === undefined) return false;
    return obj._then !== undefined;
}

export function evaluatePredicate(
    ctx: unknown,
    field: string,
    op: ConditionalOp,
    value: unknown
): boolean {
    const fieldValue =
        typeof ctx === "object" && ctx !== null
            ? (ctx as Record<string, unknown>)[field]
            : undefined;
    switch (op) {
        case "==":
            return fieldValue === value;
        case "!=":
            return fieldValue !== value;
        case "<":
            return (fieldValue as number) < (value as number);
        case "<=":
            return (fieldValue as number) <= (value as number);
        case ">":
            return (fieldValue as number) > (value as number);
        case ">=":
            return (fieldValue as number) >= (value as number);
        case "in":
            return Array.isArray(value) ? value.includes(fieldValue) : false;
        case "has":
            return Array.isArray(fieldValue)
                ? (fieldValue as unknown[]).includes(value)
                : false;
    }
}

export class ConditionalPackingStrategy implements PackingStrategy {
    canHandle(schema: BitPackerSchema): boolean {
        return isConditionalSchema(schema);
    }

    pack(
        data: unknown,
        schema: BitPackerSchema,
        context: PackingContext
    ): void {
        const cfg = schema as unknown as ConditionalSchemaShape;
        const branch = this.resolveBranch(cfg, context, data);
        if (branch === NO_BRANCH) return;
        context.packValue(data, branch as BitPackerSchema);
    }

    unpack(schema: BitPackerSchema, context: PackingContext): unknown {
        const cfg = schema as unknown as ConditionalSchemaShape;
        const branch = this.resolveBranch(cfg, context, context.parentData);
        if (branch === NO_BRANCH) return undefined;
        return context.unpackValue(branch as BitPackerSchema);
    }

    private resolveBranch(
        cfg: ConditionalSchemaShape,
        context: PackingContext,
        data: unknown
    ): BitPackerSchema | typeof NO_BRANCH {
        const predicate = cfg._if ?? cfg._when;
        if (predicate === undefined) return NO_BRANCH;
        const scope = context.parentData ?? data;
        const matched = evaluatePredicate(
            scope,
            predicate.field,
            predicate.op,
            predicate.value
        );
        if (matched) return cfg._then;
        if ("_else" in cfg) return cfg._else as BitPackerSchema;
        return NO_BRANCH;
    }
}