"""Materialize a :class:`Graph` into a dict of ``{filename: source}``.

Determinism guarantees:

  * One file per module, named ``<module>.py``.
  * Within a file, functions emitted in :attr:`Node.decl_order`.
  * Imports sorted: stdlib first (alpha), then ``from <module> import <name>``
    (alpha by module, alpha by name).
  * Pattern constants emitted only if used, in alpha order.
  * Out-edges of a node iterated in insertion order, which matters for
    ``sequential_calls`` and ``try_call_with_fallback`` semantics.

The orchestrator is a pure function: same graph in, same source out.
"""

from __future__ import annotations

from collections import defaultdict
from typing import Iterable

from graphforge.graph.schema import Edge, Graph, Node
from graphforge.materializer import codegen, patterns

HEADER = '"""Auto-generated by graphforge.materializer. Do not edit by hand."""\n'
FUTURE = "from __future__ import annotations\n"


# ---- helpers ---------------------------------------------------------


def _out_edges_in_order(graph: Graph, qualified: str) -> list[Edge]:
    """Out-edges of ``qualified`` in insertion order."""
    return [e for e in graph.edges if e.caller == qualified]


def _nodes_by_module(graph: Graph) -> dict[str, list[Node]]:
    """Map module-name -> nodes in decl_order."""
    by_mod: dict[str, list[Node]] = defaultdict(list)
    for n in graph.nodes:
        by_mod[n.module].append(n)
    for ns in by_mod.values():
        ns.sort(key=lambda n: (n.decl_order, n.name))
    return by_mod


def _cross_module_imports(graph: Graph, module: str) -> list[tuple[str, str]]:
    """``[(callee_module, callee_name), ...]`` needed by ``module``."""
    pairs: set[tuple[str, str]] = set()
    for e in graph.edges:
        caller_mod = e.caller.split(".", 1)[0]
        if caller_mod != module:
            continue
        callee_mod, callee_name = e.callee.split(".", 1)
        if callee_mod != module:
            pairs.add((callee_mod, callee_name))
    return sorted(pairs)


def _stdlib_imports_for(nodes: Iterable[Node]) -> list[str]:
    """Stdlib imports the templates in this module require."""
    needed: set[str] = set()
    for n in nodes:
        needed |= codegen.template_imports(n.body_template)
    return sorted(needed)


def _patterns_used_by(nodes: Iterable[Node]) -> list[str]:
    """Named patterns referenced by validate_with_regex nodes in this module."""
    used: set[str] = set()
    for n in nodes:
        if n.body_template == "validate_with_regex":
            name = str(n.body_template_args.get("pattern", ""))
            if patterns.get_pattern(name) is not None:
                used.add(name)
    return sorted(used)


# ---- core ------------------------------------------------------------


def materialize(graph: Graph) -> dict[str, str]:
    """Project ``graph`` to a ``{filename: source}`` map.

    Modules with zero nodes are still emitted as empty files (just header +
    future import) so that downstream import-resolution sees them.
    """
    by_mod = _nodes_by_module(graph)
    files: dict[str, str] = {}
    for module in graph.modules:
        nodes = by_mod.get(module.name, [])
        files[f"{module.name}.py"] = _render_module(graph, module.name, nodes)
    return files


def _render_module(graph: Graph, module_name: str, nodes: list[Node]) -> str:
    parts: list[str] = [HEADER, FUTURE, "\n"]

    # Stdlib imports.
    for imp in _stdlib_imports_for(nodes):
        parts.append(f"import {imp}\n")

    # Cross-module function imports.
    for callee_mod, callee_name in _cross_module_imports(graph, module_name):
        parts.append(f"from {callee_mod} import {callee_name}\n")

    if (
        any(_stdlib_imports_for(nodes))
        or _cross_module_imports(graph, module_name)
    ):
        parts.append("\n")

    # Pattern constants used in this module. We emit a plain string literal
    # (not a raw-string-prefixed one) because ``repr()`` already produces a
    # valid Python string literal — wrapping it in ``r"..."`` would double
    # the backslashes and break regex metacharacters like ``\s`` and ``\d``.
    used_patterns = _patterns_used_by(nodes)
    for name in used_patterns:
        regex = patterns.get_pattern(name)
        constant = patterns.constant_name(name)
        parts.append(f"{constant} = {regex!r}\n")
    if used_patterns:
        parts.append("\n")

    # Functions.
    for i, node in enumerate(nodes):
        out_edges = _out_edges_in_order(graph, node.qualified_name)
        body = codegen.render_body(node, out_edges, graph)
        parts.append(f"def {node.name}{node.signature}:\n{body}\n")
        if i != len(nodes) - 1:
            parts.append("\n")

    source = "".join(parts)
    # Ensure exactly one trailing newline.
    return source.rstrip("\n") + "\n"