class BuildNode:

    def __init__(self, name, cmd, deps=None, cache_key=None):

        self.name = name
        self.cmd = cmd
        self.deps = deps or []
        self.cache_key = cache_key

    def __repr__(self):
        return f"<BuildNode {self.name}>"


class BuildGraph:

    def __init__(self, spec):

        self.spec = spec
        self.nodes = []

    # -----------------------------
    # ENTRY POINT
    # -----------------------------
    def generate(self):

        self._fetch_source()
        self._resolve_toolchain()
        self._compile_units()
        self._link_stage()
        self._package()
        self._cache()

        return self.nodes

    # -----------------------------
    # STAGES
    # -----------------------------
    def _fetch_source(self):

        self.nodes.append(
            BuildNode(
                name="fetch_source",
                cmd="git clone repo",
                cache_key="src"
            )
        )

    def _resolve_toolchain(self):

        cmd = f"setup-toolchain --arch {self.spec.arch} --target {self.spec.target}"

        self.nodes.append(
            BuildNode(
                name="resolve_toolchain",
                cmd=cmd,
                deps=["fetch_source"],
                cache_key="toolchain"
            )
        )

    def _compile_units(self):

        # simplified fan-out model (real version would parse AST / Makefile / Ninja)
        for i in range(3):

            self.nodes.append(
                BuildNode(
                    name=f"compile_unit_{i}",
                    cmd=f"{self.spec.toolchain} -c file_{i}.c",
                    deps=["resolve_toolchain"],
                    cache_key=f"obj_{i}"
                )
            )

    def _link_stage(self):

        self.nodes.append(
            BuildNode(
                name="link",
                cmd=f"{self.spec.toolchain} link *.o -o output.elf",
                deps=["compile_unit_0", "compile_unit_1", "compile_unit_2"],
                cache_key="binary"
            )
        )

    def _package(self):

        self.nodes.append(
            BuildNode(
                name="package",
                cmd=f"package --format {self.spec.output_mode}",
                deps=["link"],
                cache_key="artifact"
            )
        )

    def _cache(self):

        self.nodes.append(
            BuildNode(
                name="cache_upload",
                cmd="upload-cache",
                deps=["package"],
                cache_key="cache"
            )
        )